Fabrication of integrated devices (“ICs”), for example, and without limitation, semiconductor ICs, is complicated and, because of increasingly stringent requirements on device designs due to demands for greater device speed, fabrication is becoming ever more complicated. Today's fabrication facilities are routinely producing devices having 0.13 μm feature sizes, and tomorrow's facilities soon will be producing devices having even smaller feature sizes.
For ICs having minimum feature sizes of 0.13 μm and below, problems of RC delay and crosstalk become significant. For example, device speed is limited in part by the RC delay which is determined by the resistance of metal used in an interconnect scheme and the dielectric constant of insulating dielectric material used between metal interconnects. In addition, with decreasing geometries and device sizes, the semiconductor industry has sought to avoid parasitic capacitance and crosstalk caused by inadequate insulating layer in the ICs. One way to achieve the desired low RC delay and higher performance in ICs involves using dielectric materials in the insulating layers that have a low dielectric constant (“low-k” materials). Such materials are fabricated by depositing a material having a low dielectric constant (for example, and without limitation, a carbon-doped oxide (“CDO”)), and by treating the deposited material using an electron beam, for example, and without limitation, an electron beam provided by an electron beam treatment apparatus such as that disclosed in U.S. Pat. No. 5,003,178 (the '178 patent).
As the thickness of films such as, for example, and without limitation, dielectric films, decreases, the energy of electrons used to treat such films necessarily must decrease. For an electron beam treatment apparatus fabricated in accordance with the '178 patent, in order for the energy to decrease, a cathode voltage used to accelerate electrons generated in a generation and acceleration region between a cathode and an anode must also decrease. For example, for a 1 μm thick film having a density of about 1.3 gm/cm3, the cathode voltage may be about 6.5 KV; for a 5000 Å thick film, the cathode voltage may be about 4 KV; and for a 2,500 Å thick film, the cathode voltage may be about 2 KV. However, we have found that for (i) a particular cathode-anode spacing, (ii) a particular value of electron beam current, and (iii) a particular type of gas in the apparatus; as the cathode voltage is reduced, the pressure of the gas in the electron beam treatment apparatus must increase. We believe this is so because: (a) as the cathode voltage is reduced, a larger number of ions is required to create enough electrons at the cathode to sustain the electron beam current; (b) a larger pressure is required to enable production of the larger number of ions; and (c) the yield of electrons from the cathode is lower at lower cathode voltage.
However, as taught by the '178 patent, cathode-anode spacing (also referred to in the '178 patent as a working distance) needs to be less than an electron mean free path in the gas to prevent breakdown (i.e., arcing or spark formation). As is known, the electron mean free path (λ): (a) is inversely proportional to gas pressure; and (b) it decreases as cathode voltage decreases. Thus, in accordance with the teaching of the '178 patent, to treat thinner films, the cathode voltage decreases, the pressure increases, and the working distance decreases. However, small working distances may become problematic in certain applications such as, for example and without limitation, applications wherein 300 mm wafers are treated and including such applications wherein the wafers are heated. In such applications, for small working distances, the anode may be so large that bowing or warping may become a problem.
In light of the above, there is a need for an electron treatment apparatus that can operate at working distances that are larger than the electron mean free path.